An optical measuring apparatus irradiates a measuring target face with a measuring light beam and receives the measuring light beam reflected by the measuring target face so as to obtain information about displacement and shape of the measuring target face contained in the reflected measuring light beam. However, direct irradiation of the measuring target face with the measuring light beam makes high-accuracy measurement difficult due to reflection characteristics and influence of inclination of the measuring target face. Accordingly, various measuring probes having a function to move in conformity to the measuring target face and a function to reflect the measuring light beam have conventionally been proposed.
For example, in Japanese publication of unexamined patent application No. 2000-283747, a measuring probe having two parallel plate springs has been disclosed. Base ends of the plate springs are fixed to a mainframe of an optical measuring apparatus while top ends thereof are equipped with a contact portion which comes into contact with a measuring target face. A reflecting plane for reflecting a measuring light beam is provided on a back face of the contact portion. The contact portion is resiliently pressed to the measuring target face by the plate springs so as to displace in compliance with projections and depressions of the measuring target face and deformation thereof.
Moreover, in Japanese publication of unexamined patent application No. H06-265340, there has been disclosed a measuring probe having an air slide portion movable in vertical direction, in which a contact portion is mounted on a lower end of the air slide portion and an upper end thereof serves as a reflecting plane. Such an air slide portion is supported by a spring.
Moreover, in Japanese publication of unexamined patent application No. H04-98114, a measuring probe shown in FIG. 11 has been disclosed. The measuring probe is composed of: a cylindrical housing 101; an air bearing 102 provided inside the housing 101; a probe shaft 103 supported by the air bearing 102 movably in an axial direction thereof; a stylus 104 which comes into contact with a measuring target face at a front end of the probe shaft 103; a stopper 105 for regulating movement of the probe shaft 103 in the axial direction; a length measuring portion 106 having a corner cube 106a provided on a rear end portion of the probe shaft 103 for detecting a moving amount of the probe shaft 103; a contact pressure regulating portion 107 provided on the rear end portion of the probe shaft 103 and the inside of the housing 101; a contact pressure detecting portion 108 provided in between the probe shaft 103 and the stopper 105 for detecting a contact pressure of the stylus 104 upon the measuring target object; and a contact pressure control portion 109 for optimizing the contact pressure for the contact pressure regulating portion 107 based on a detection result of the output voltage 108.
The housing 101 has: a first housing portion 110 encircling the corner cube 106a; a second housing portion 111 connected to the first housing portion 110 for retaining the contact pressure regulating portion 107; a third housing portion 112 connected to the second housing portion 111 for retaining the air bearing 102; a fourth housing portion 113 connected to the third housing portion 112 for concentrically encircling the contact pressure detecting portion 108; and a fifth housing portion 114 which is connected to the fourth housing portion 113 and has the stopper 105 concentrically inserted thereinto. It is to be noted that in the contact pressure regulating portion 107, a core 115 is provided on the probe shaft 103 and permanent magnets 116, 117, coils 118, 119, collar-shaped fins 120 for releasing heat of the coils 118, 119 and the like are provided on the side of the second housing portion 111.
However, these conventional measuring probes have following problems.
In the invention disclosed in the Japanese publication of unexamined patent application No. 2000-283747, while it is essential for accurate measurement that the reflecting plane of the contact portion is perpendicular to the measuring light beam, the projections and depressions of the measuring target object cause subtle changes in an angle of the reflecting plane of the measuring probe and therefore it becomes difficult to constantly irradiate the reflecting plane with a perpendicular measuring light beam. Moreover, when the measuring probe is replaced, it is difficult to set the reflecting plane to be perpendicular to the measuring light beam.
Moreover, in the invention disclosed in the Japanese publication of unexamined patent application No. H06-265340, the air slide and the spring to support the weight of the air slide are used and therefore the measuring probe cannot be disposed in horizontal direction.
Moreover, in the inventions disclosed in the Japanese publication of unexamined patent application No. 2000-283747 and the Japanese publication of unexamined patent application No. H06-265340, both the measuring probes do not have mechanisms to move the contact portions by very small distances with respect to the measuring target faces. Therefore, at the start of measurement, it is necessary to force the contact portions to run upon edge of the measuring target objects so as to dispose the contact portions on the measuring target faces. Consequently, damages on the measuring target face or force acting in direction perpendicular to the measuring direction may cause failures of the springs or the contact portions of the measuring probes.
Moreover, in the case of the measuring probe disclosed in the Japanese publication of unexamined patent application No. H04-98114, it is unclear if magnetic force generated by application of current to the coil operates in the state of being focused on a magnetic substance since materials of the contact pressure regulating portion 107 and members constituting its periphery are not identified. Further, as described above, the housing 101 serving as a fixed member is assembled by connecting five members in sequence, which requires screws necessary for the assembling and female screws corresponding to the screws, thereby making downsizing difficult and increasing external dimensions of the housing. This upsizes the measuring probe and increases heat capacity of the probe. Consequently, a long period of time is necessary for the temperature of the measuring probe to become constant after power is turned on and therefore a standby time till start of measurement is lengthened. Further, in consideration of measuring a convex lens and a concave lens, the length of the probe shaft should be increased, which promotes inclination of the probe shaft and the reflecting plane due to frictional resistance against the measuring target face during measurement, thereby causing a problem that an optical axis toward the corner cube 106a is displaced to cause instable measurement.